The present invention relates generally to the field of methods and medical devices for modulating cardiac muscle activity and contractility and more specifically to methods and devices for setting the parameters of a detection time window used for initiating the delivery of excitable tissue controller (ETC) signals under a variety of conditions including varying heart rates, paced or sensed beats and the absence and presence of ETC signals"" effects on the velocity of propagation of a cardiac depolarization wave.
Excitable tissue controllers (ETCs) are devices which modulate the activity of excitable tissues by application of non-excitatory electrical stimulation to the excitable tissue through suitable electrodes in contact with the tissue. For example, ETC devices may be used, inter alia, to increase or decrease the contractility of cardiac muscle in vitro, in vivo and in situ., as disclosed in detail in PCT application, International Publication Number WO 97/25098 to Ben-Haim et al., titled xe2x80x9cELECTRICAL MUSCLE CONTROLLERxe2x80x9d, incorporated herein by reference. Other methods and applications of ETC devices are disclosed in PCT applications commonly-assigned to the assignee of the present application, International Publication Number WO 98/10828, titled xe2x80x9cAPPARATUS AND METHOD FOR CONTROLLING THE CONTRACTILITY OF MUSCLESxe2x80x9d to Ben Haim et al., incorporated herein by reference, International Publication Number WO 98/10829, titled xe2x80x9cDRUG-DEVICE COMBINATION FOR CONTROLLING THE CONTRACTILITY OF MUSCLESxe2x80x9d to Ben Haim et al., incorporated herein by reference and International Publication Number WO 98/10830, titled xe2x80x9cFENCING OF CARDIAC MUSCLESxe2x80x9d to Ben Haim et al., incorporated herein by reference, International Publications Number WO 98/10831 to Ben Haim et al., titled xe2x80x9cCARDIAC OUTPUT CONTROLLERxe2x80x9d, incorporated herein by reference.
Further applications of the ETC including devices combining cardiac pacing and cardiac contractility modulation are disclosed in PCT Application, International Publication No. WO 98/10832, titled xe2x80x9cCARDIAC OUTPUT ENHANCED PACEMAKERxe2x80x9d to Ben Haim et al., co-assigned to the assignee of the present application. Such ETC devices function by applying non-excitatory electrical field signals of suitable amplitude and waveform, appropriately timed with respect to the heart""s intrinsic electrical activity to selected cardiac segments. The contraction of the selected segments can be modulated to increase or decrease the stroke volume of the heart. The timing of the ETC signals must be carefully controlled since application of the ETC signal to the myocardium at inappropriate times may be arrhythmogenic. The ETC signals must therefore be applied to the selected cardiac segment within a defined time interval during which the selected cardiac segment will not be stimulated by the ETC signals.
As disclosed in International Publication No. WO 98/10832, the ETC signals may be timed relative to a trigger signal which is also used as a pacing trigger, or may be timed relative to locally sensed electrogram signals.
U.S. patent application Ser. No. 09/276,460, to Mika et al., entitled xe2x80x9cAPPARATUS AND METHOD FOR TIMING THE DELIVERY OF NON-EXCITATORY ETC SIGNALS TO A HEARTxe2x80x9d, filed Mar. 25, 1999 and assigned to the common assignee of the present application, now U.S. Pat. No. 6,263,242, the entire specification of which is incorporated herein by reference, and the corresponding PCT international application PCT/IL00/00126, International Publication Number WO 00/57952, disclose a method for timing the delivery of non-excitatory ETC signals to a heart using, inter alia, an alert window period for reducing the probability of delivering an improperly timed ETC signal to the heart due to spurious detection of noise or ectopic beats.
The methods of timing of the delivery of ETC signals disclosed hereinabove do not take into account the fact that naturally occurring and pacemaker induced changes in heart rate (HR) may cause changes in the velocity of propagation of the depolarization wave in the myocardium. Additionally, the delivery of the ETC signals to the myocardium may also cause changes in the velocity of propagation of the depolarization wave in the myocardium. Other factors such as, inter alia, various cardio-active drug treatments and myocardial pathological conditions such as ischemia may also cause changes in the velocity of propagation of the depolarization wave in the myocardium. It is therefore desirable to have a method for determining proper timing of the delivery of ETC signals which takes into account variations in velocity of propagation of the depolarization wave in the myocardium under different cardiac conditions.
There is therefore provided, in accordance with a preferred embodiment of the present invention, a method for setting the parameters of an alert time window in an excitable tissue control device operative under a plurality of different cardiac conditions of a heart of a patient. The method includes the step of providing the excitable tissue control device with a set of data. The set of data includes a plurality of sets of alert time window parameters. Each set of alert time window parameters is associated with one of the plurality of different cardiac conditions. Each set of alert time window parameters includes at least a set of timing parameters usable for obtaining a beginning time point and an ending time point for the alert time window. Each set of the plurality of sets of alert time window parameters is obtained by processing data collected from a plurality of cardiac beats of the heart of the patient under the plurality of different cardiac conditions within a data collection session prior to the step of providing. The method further includes the step of automatically selecting, for a current beat cycle of the heart, a current set of alert time window parameters of the plurality of sets of alert time window parameters based on the current cardiac conditions detected for the current beat cycle. The method further includes the step of using, for the current beat cycle, the current set of alert time window parameters selected in the step of automatically selecting to start and terminate the alert time window based on the time of detecting a first depolarization event at or about a first cardiac site. The method further includes the steps of detecting, within the duration of the alert time window of the current beat cycle, a second depolarization event at a second cardiac site of the heart, and triggering the delivery of a delayed non-excitatory excitable tissue control signal at or about the second cardiac site based on the time of detection of the second depolarization event.
There is further provided, in accordance with a preferred embodiment of the present invention, a method for setting the parameters of an alert time window in an excitable tissue control device operative under a plurality of different cardiac conditions of a heart of a patient. The method includes the step of providing the excitable tissue control device with a set of data. The set of data includes a plurality of sets of alert time window parameters. Each set of alert time window parameters is uniquely associated with a different set of values of a plurality of cardiac condition defining parameters identifying one of the plurality of different cardiac conditions. Each set of alert time window parameters of the plurality of sets of alert time window parameters includes at least a set of timing parameters usable for obtaining a beginning time point and an ending time point for the alert time window. Each set of alert time window parameters is obtained by processing data collected from a plurality of cardiac beats of the heart of the patient under the plurality of different cardiac conditions within a data collection session prior to the step of providing. The method further includes the step of updating for a current beat cycle of the heart the values of a plurality of cardiac condition defining variables corresponding to the cardiac condition defining parameters. The method further includes the step of automatically selecting for the current beat cycle a current set of alert time window parameters of the plurality of sets of alert time window parameters based on the current values of the cardiac condition defining variables. The method further includes the step of using, for the current beat cycle, the current set of alert time window parameters selected in the step of automatically selecting to start and terminate the alert time window based on the time of detecting a first depolarization event at or about a first cardiac site. The method further includes the steps of detecting within the duration of the alert time window of the current beat cycle a second depolarization event at a second cardiac site of the heart, and triggering the delivery of a delayed non-excitatory excitable tissue control signal at or about the second cardiac site based on the time of detection of the second depolarization event.
There is also provided, in accordance with a preferred embodiment of the present invention, an excitable tissue control device for setting, on a beat by beat basis, the parameters of an alert time window under a plurality of different cardiac conditions of a heart of a patient. The device includes a plurality of electrodes implanted in or about the heart. The device further includes detection circuitry for detecting electrical depolarization events in a first cardiac site through at least a first electrode of the plurality of electrodes. The first electrode is disposed in or about the first cardiac site. The detection circuitry is also used for detecting electrical depolarization events in a second cardiac site through at least a second electrode of the plurality of electrodes. The second electrode is disposed in or about the second cardiac site. The device further includes an excitable tissue control unit for delivering non-excitatory excitable tissue control signals to at least part of the second cardiac site through one or more electrodes of the plurality of electrodes. The device further includes a memory unit for storing a set of data. The set of data includes a plurality of sets of alert time window parameters. Each set of alert time window parameters is uniquely associated with a different set of values of a plurality of cardiac condition defining parameters identifying one of the plurality of different cardiac conditions. Each set of alert time window parameters includes at least a set of timing parameters usable for obtaining a beginning time point and an ending time point for the alert time window. Each set of alert time window parameters is obtained by processing data collected from a plurality of cardiac beats of the heart of the patient under the plurality of different cardiac conditions within a data collection session performed in the patient. The device further includes a processor unit operatively connected to the detection circuitry, the excitable tissue control unit and the memory unit. The processor unit is usable for receiving detection signals from the detection circuitry, for controlling the excitable tissue control unit by using the received detection signals, for updating in a current beat cycle of the heart the values of a plurality of cardiac condition defining variables corresponding to the cardiac condition defining parameters, for automatically selecting for the current beat cycle a current set of alert time window parameters of the plurality of sets of alert time window parameters based on the current values of the cardiac condition defining variables, for applying the current set of alert time window parameters to start the alert time window within the current beat cycle after detecting a first depolarization event at or about the first cardiac site and to terminate the alert time window, and for initiating the delivery of a delayed excitable tissue control signal at or about the second cardiac site upon detecting, within the duration of the alert time window, a depolarization event in or about the second cardiac site of the heart. The device further includes a power source for providing power to the detection circuitry, the processor unit the memory unit and the excitable tissue control unit.
Furthermore, in accordance with another preferred embodiment of the present invention, the device further includes a telemetry unit operatively connected to the power source and the processor unit for telemetrically receiving data from a second telemetry unit disposed outside the patient.
Furthermore, in accordance with another preferred embodiment of the present invention, the plurality of sets of alert time window parameters of the set of data are stored in the memory unit as a data array or a look up table.
Furthermore, in accordance with another preferred embodiment of the present invention, the detection circuitry is adapted for being controllably switched between a plurality of detection sensitivity levels, and each set of alert time window parameters of the plurality of sets of alert time window parameters further includes at least one detection sensitivity parameter having a value representing one of the plurality of detection sensitivity levels of the detection circuitry, and the processor unit is adapted for using the value of the at least one detection sensitivity parameter of the current beat cycle to switch the detection circuitry to a detection sensitivity level represented by the at least one detection sensitivity parameter of the current beat cycle.
Furthermore, in accordance with another preferred embodiment of the present invention, the detection circuitry is adapted for being switched between a plurality of voltage threshold levels and the at least one detection sensitivity parameter includes a voltage threshold level.
Furthermore, in accordance with another preferred embodiment of the present invention, the detection circuitry is adapted for performing event detection based on a morphological detection method and wherein the at least one detection sensitivity parameter includes at least one morphological detection parameter.
Furthermore, in accordance with another preferred embodiment of the present invention, the set of data is a degenerate set of data in which at least some of the sets of alert time window parameters of the plurality of sets of alert time window parameters have identical values of the at least one detection sensitivity parameter.
Furthermore, in accordance with another preferred embodiment of the present invention, the plurality of cardiac conditions includes beats having a plurality of different beat to beat time intervals representing different instantaneous heart rates of the heart.
Furthermore, in accordance with another preferred embodiment of the present invention, the plurality of cardiac conditions further includes beats occurring during a time period in which the prior application of excitable tissue control signals results in a change of the velocity of propagation of a depolarization wave in at least a portion of the myocardial tissue disposed between the first cardiac site and the second cardiac site of the heart, and beats occurring during a time period in which the prior application of excitable tissue control signals does not result in a change in the velocity of propagation of a depolarization wave in at least a portion of the myocardial tissue disposed between the first cardiac site and the second cardiac site of the heart.
Furthermore, in accordance with another preferred embodiment of the present invention, the device further includes a pacing unit operatively connected to the power source, the processor unit and to at least one electrode of the plurality of electrodes, for delivering pacing pulses to the heart through the at least one electrode.
Furthermore, in accordance with another preferred embodiment of the present invention, the plurality of cardiac conditions includes beats initiated by the natural pacemaker of the heart and beats initiated by a pacing pulse delivered by the excitable tissue control device.
Furthermore, in accordance with another preferred embodiment of the present invention, the set of timing parameters of the alert time window parameters includes a beginning time point value and an ending time point value for the alert time window.
Furthermore, in accordance with another preferred embodiment of the present invention, the excitable tissue control device is provided with a value of the bin duration of a time bin used for collecting data within the data collection session. The value is stored in the memory unit. The set of timing parameters of the alert time window parameters includes a starting bin number and an ending bin number, and the processor unit is adapted for computing the starting time point and ending time point of the alert time window from the bin duration, the starting bin number and the ending bin number, prior to starting of the alert time window within the current beat cycle.
Furthermore, in accordance with another preferred embodiment of the present invention, the set of timing parameters includes a set of approximation parameters and wherein the processing of the data collected from the heart in the data collection session includes using an approximation method to obtain a plurality of sets of approximation parameters usable for computing improved approximated values of the beginning time point and the ending time point of the alert time window.
Furthermore, in accordance with another preferred embodiment of the present invention, the approximation method is a linear piecewise approximation method. The set of approximation parameters includes a beginning time point parameter and a first slope parameter associated with the beginning time point parameter. The set of approximation parameters also includes an ending time point parameter and a second slope parameter associated with the ending time point parameter. The step of using includes computing an approximated beginning time point for the alert time window of the current beat cycle from the values of the current cycle length measured for the current beat cycle, the first slope parameter and the beginning time point parameter, and computing an approximated ending time point for the alert time window of the current beat cycle from the values of the current cycle length, the second slope parameter and the ending time point parameter.
Furthermore, in accordance with another preferred embodiment of the present invention, the current cycle length is the instantaneous cycle length determined from the current Rxe2x80x94R interval or the current Axe2x80x94A interval measured for the current beat cycle.
Furthermore, in accordance with another preferred embodiment of the present invention, the current cycle length is an average cycle length computed from the values of a plurality of consecutive Rxe2x80x94R intervals including the Rxe2x80x94R interval of the current beat cycle.
Furthermore, in accordance with another preferred embodiment of the present invention, the current cycle length is an average cycle length computed from the values of a plurality of consecutive Axe2x80x94A intervals including the Axe2x80x94A interval of the current beat cycle.
Furthermore, in accordance with another preferred embodiment of the present invention, the set of data is a degenerate set of data in which at least some of the sets of alert time window parameters of the plurality of sets of alert time window parameters have identical values of the set of timing parameters.
Furthermore, in accordance with another preferred embodiment of the present invention, the first cardiac site is the right ventricle of the heart and the second cardiac site is the left ventricle of the heart.
Furthermore, in accordance with another preferred embodiment of the present invention, the first cardiac site is the right atrium of the heart and the second cardiac site is the left ventricle of the heart.
Furthermore, in accordance with another preferred embodiment of the present invention, the excitable tissue control device is implanted in the patient.
Furthermore, in accordance with another preferred embodiment of the present invention, the excitable tissue control device is disposed out of the patient and is operatively connected to the plurality of electrodes implanted in or about the heart of the patient.
There is also provided, in accordance with a preferred embodiment of the present invention, an excitable tissue control device for setting on a beat by beat basis the parameters of an alert time window under a plurality of different cardiac conditions of a heart of a patient. The device includes a plurality of electrodes implanted in or about the heart. The device also includes means for detecting electrical depolarization events in a first cardiac site through at least a first electrode disposed in or about the first cardiac site, and for detecting electrical depolarization events in a second cardiac site through at least a second electrode disposed in or about the second cardiac site. The device also includes excitable tissue control means for delivering non-excitatory excitable tissue control signals to at least part of the second cardiac site through one or more electrodes of the plurality of electrodes. The device also includes memory means for storing a set of data. The set of data includes a plurality of sets of alert time window parameters. Each set of alert time window parameters is uniquely associated with a different set of values of a plurality of cardiac condition defining parameters identifying one of the plurality of different cardiac conditions. Each set of alert time window parameters includes at least a set of timing parameters usable for obtaining a beginning time point and an ending time point for the alert time window. Each set of alert time window parameters is obtained by processing data collected from a plurality of cardiac beats of the heart of the patient under the plurality of different cardiac conditions within a data collection session performed in the patient. The device also includes processing means operatively connected to the detection means, the excitable tissue control means and the memory means. The processing means are used for receiving detection signals from the detection means, for controlling the excitable tissue control means by using the received detection signals, for updating in a current beat cycle of the heart the values of a plurality of cardiac condition defining variables corresponding to the cardiac condition defining parameters, for automatically selecting for the current beat cycle a current set of alert time window parameters of the plurality of sets of alert time window parameters based on the current values of the cardiac condition defining variables, for applying the current set of alert time window parameters to start the alert time window within the current beat cycle after detecting a first depolarization event at or about the first cardiac site and to terminate the alert time window, and for initiating the delivery of a delayed excitable tissue control signal at or about the second cardiac site upon detecting within the duration of the alert time window a depolarization event in or about the second cardiac site of the heart. The device also includes a power source for providing power to the detection means, the processing means the memory means and the excitable tissue control means.
Furthermore, in accordance with another preferred embodiment of the present invention, the device further includes telemetry means operatively connected to the power source and the processing means for telemetrically receiving data from a second telemetry means disposed outside the patient.
Finally, in accordance with another preferred embodiment of the present invention, the device further includes pacing means operatively connected to the power source, the processing means and to at least one electrode of the plurality of electrodes, for delivering pacing pulses to the heart through the at least one electrode.